[SCSI] Use ARRAY_SIZE in spi_print_msg

Replace the custom NO_*_MSGS definitions with uses of ARRAY_SIZE.
This fixes a bug in the definition of NO_EXTENDED_MSGS.

Signed-off-by: Matthew Wilcox <matthew@wil.cx>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>