keysym-utf: Fix a warning about shadowing

Change variable names to avoid the name clash. The warning seen is

src/keysym-utf.c: In function 'bin_search':
src/keysym-utf.c:841: warning: declaration of 'min' shadows a global declaration
src/utils.h:109: warning: shadowed declaration is here
src/keysym-utf.c:842: warning: declaration of 'max' shadows a global declaration
src/utils.h:115: warning: shadowed declaration is here

Signed-off-by: Siddharth Heroor <heroor@ti.com>