Fix bug in PCI driver with not saved registers

In the PCI driver's device enumeration function, there was a mistake
where a register that is being used in that function wasn't preserved
as it should've been. It didn't cause any errors (at least yet), but
it's better to fix such stuff once found.

i386/legacy-boot/src-asm/drivers/pci/driver.asm

@@ -34,7 +34,7 @@ initialize_pci_driver:
 
     push ebp
     mov ebp, esp
-    push ebx
+    push dword PCI_DEVICE_COUNT_OFFSET
     push dword 2
     push dword 0
     push dword 0

i386/legacy-boot/src-asm/drivers/pci/enumerate.asm

@@ -190,11 +190,12 @@ pci_enumerate_bus:
 
     mov         [esi + (64 - 8)],       ebx
     mov         [esi + (64 - 12)],      ecx
+    mov         [esi + (64 - 16)],      edx
     mov         [esi + (64 - 20)],      edi
     ; [esi]:        Device-in-bus Index
     ; [esi + 4]:    Number of existing devices
     ; [esi + 8]:    Bus number
-    ; [esi + 12]:   
+    ; [esi + 12]:   PCI driver area pointer
     mov         [esi],                  dword 0
     mov         [esi + 4],              dword 0
     mov         eax,                    [ebp - 8]
@@ -259,6 +260,7 @@ pci_enumerate_bus:
 .epilog:
     mov         ebx,                    [esi + (64 - 8)]
     mov         ecx,                    [esi + (64 - 12)]
+    mov         edx,                    [esi + (64 - 16)]
     mov         edi,                    [esi + (64 - 20)]
 
     mov         eax,                    [esi + 4]
@@ -313,7 +315,6 @@ pci_enumerate:
     cmp         edx,                    [ebp - 8]
     jae         .epilog
 
-
 .call_bus_enumerator:
     push        ebp
     mov         ebp,                    esp