src/include: Fix unsigned warnings

Fix warning detected by checkpatch.pl:

WARNING: Prefer 'unsigned int' to bare use of 'unsigned'

BRANCH=none
BUG=None
TEST=Build and run on Galileo Gen2

Change-Id: I23d9b4b715aa74acc387db8fb8d3c73bd5cabfaa
Signed-off-by: Lee Leahy <Leroy.P.Leahy@intel.com>
Reviewed-on: https://review.coreboot.org/18607
Reviewed-by: Philippe Mathieu-Daudé <philippe.mathieu.daude@gmail.com>
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Martin Roth <martinroth@google.com>
diff --git a/src/include/pc80/mc146818rtc.h b/src/include/pc80/mc146818rtc.h
index 99fba9d..9f4eb5a 100644
--- a/src/include/pc80/mc146818rtc.h
+++ b/src/include/pc80/mc146818rtc.h
@@ -184,7 +184,8 @@
 
 enum cb_err set_option(const char *name, void *val);
 enum cb_err get_option(void *dest, const char *name);
-unsigned read_option_lowlevel(unsigned start, unsigned size, unsigned def);
+unsigned int read_option_lowlevel(unsigned int start, unsigned int size,
+	unsigned int def);
 
 #else /* defined(__ROMCC__) */
 #include <drivers/pc80/rtc/mc146818rtc_early.c>