fbcon: replace mono_col macro with static inline

fbcon: replace mono_col macro with static inline

Use __u32 for max_len to match the declaration of length in the struct
fb_bitfield.

Suppresses sparse shadowed variable warnings from the nested max()
macros:
drivers/video/console/fbcon.h:130:8: warning: symbol '_x' shadows an earlier one
drivers/video/console/fbcon.h:130:8: originally declared here
drivers/video/console/fbcon.h:130:8: warning: symbol '_x' shadows an earlier one
drivers/video/console/fbcon.h:130:8: originally declared here
drivers/video/console/fbcon.h:130:8: warning: symbol '_y' shadows an earlier one
drivers/video/console/fbcon.h:130:8: originally declared here

[akpm@linux-foundation.org: fix constness]
Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>