time: Fix signedness bug in sysfs_get_uname() and its callers

sysfs_get_uname() is erroneously declared as returning size_t even
though it may return a negative value, specifically -EINVAL.  Its
callers then check whether its return value is less than zero and indeed
that is never the case for size_t.

This patch changes sysfs_get_uname() to return ssize_t and makes sure
its callers use ssize_t accordingly.

Signed-off-by: Patrick Palka <patrick@parcs.ath.cx>
[jstultz: Didn't apply cleanly, as a similar partial fix was also applied
so had to resolve the collisions]
Signed-off-by: John Stultz <john.stultz@linaro.org>

kernel/time/clocksource.c

@@ -909,7 +909,7 @@ sysfs_show_current_clocksources(struct device *dev,
 	return count;
 }
 
-size_t sysfs_get_uname(const char *buf, char *dst, size_t cnt)
+ssize_t sysfs_get_uname(const char *buf, char *dst, size_t cnt)
 {
 	size_t ret = cnt;