profile: Use vzalloc() rather than vmalloc() & memset()

There's no reason to memset() manually when we have vzalloc().

Signed-off-by: Jesper Juhl <jj@chaosbits.net>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: William Irwin <wli@holomorphy.com>
LKML-Reference: <alpine.LNX.2.00.1010302150310.1572@swampdragon.chaosbits.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>