tinymix: Improve detect of integer values

Tinymix detected integer values when setting controls simply by calling
isdigit on the first character of the value being set. This causes
problems with enumerated controls whos values start with digits. This
patch improves this to provide more robust detection of integer values.
Merge branch 'master' of git://github.com/charleskeepax/tinyalsa into charleskeepax-master

Conflicts:
	tinymix.c
Merge branch 'charleskeepax-master'