alpha: fix the BUG() macro

The commit "alpha: teach the compiler that BUG doesn't return"
(ed6b9b97f42c091630335bfb71a2931e6f86388b) moved the asm code into inline
function which takes __FILE__ and __LINE__ as arguments.  This violates
asm constrains there ("i" - an immediate operand with constant value), so
that compile may result in warning or error, depending on compiler
version.

Just adding an infinite loop to the BUG() is sufficient.

Signed-off-by: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Richard Henderson <rth@twiddle.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>