platform/x86: ibm_rtl: fix EBDA signature search pointer arithmetic

platform/x86: ibm_rtl: fix EBDA signature search pointer arithmetic

The ibm_rtl_init() function searches for the signature but has a pointer
arithmetic error. The loop counter suggests searching at 4-byte intervals
but the implementation only advances by 1 byte per iteration.

Fix by properly advancing the pointer by sizeof(unsigned int) bytes
each iteration.

Reported-by: Yuhao Jiang <danisjiang@gmail.com>
Reported-by: Junrui Luo <moonafterrain@outlook.com>
Fixes: 35f0ce032b0f ("IBM Real-Time "SMI Free" mode driver -v7")
Signed-off-by: Junrui Luo <moonafterrain@outlook.com>
Link: https://patch.msgid.link/SYBPR01MB78812D887A92DE3802D0D06EAFA9A@SYBPR01MB7881.ausprd01.prod.outlook.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>