ARC: uaccess: dont use "l" gcc inline asm constraint modifier

This used to setup the LP_COUNT register automatically, but now has been
removed.

There was an earlier fix 3c7c7a2f which fixed instance in delay.h but
somehow missed this one as gcc change had not made its way into
production toolchains and was not pedantic as it is now !

Cc: stable@vger.kernel.org
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>