libbb: make trim() return pointer to terminating NUL

function                                             old     new   delta
trim                                                  80      90     +10
angle_address                                         56      50      -6
sysctl_main                                          282     273      -9
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/3 up/down: +10/-15)           Total:  -5 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/include/libbb.h b/include/libbb.h
index 6a2a2d6..6077f64 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -347,7 +347,7 @@
 unsigned monotonic_sec(void) FAST_FUNC;
 
 extern void chomp(char *s) FAST_FUNC;
-extern void trim(char *s) FAST_FUNC;
+extern char *trim(char *s) FAST_FUNC;
 extern char *skip_whitespace(const char *) FAST_FUNC;
 extern char *skip_non_whitespace(const char *) FAST_FUNC;
 extern char *skip_dev_pfx(const char *tty_name) FAST_FUNC;