[SCSI] arcmsr: fix misuse of | instead of &

ARCMSR_ARC1880_DiagWrite_ENABLE is 0x00000080 so (x | 0x00000080) is
never zero.  The intent here was to test that loop until
ARCMSR_ARC1880_DiagWrite_ENABLE was turned on, but because the test was
wrong, we would do five loops regardless of whether it succeed or not.

Also I simplified the condition a little by removing the unused
assignement.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Nick Cheng <nick.cheng@areca.com.tw>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>