i965: Fix glTexImage when packing alignment != cpp

i965: Fix glTexImage when packing alignment != cpp

Fixes texture corruption of Weston clients on cairo-glesv2 backend.
Commit 49ed599 introduced the bug.

Corruption occured when glTexSubImage called
intel_texsubimage_tiled_memcpy() with:
  x,y=10,9
  w,h=7,7
  format=GL_ALPHA(0x1906)
  type=GL_UNSIGNED_BYTE(0x1401)
  gl_format=MESA_FORMAT_A8(0x18)
  packing.alignemnt=4

The function miscalculated the source image's stride as w*cpp=7 without
taking into account the packing alignment. The actual stride was 8.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=70435
Reported-by: U. Artie Eoff <ullysses.a.eoff@intel.com>
Tested-by: Kristian Høgsberg <krh@bitplanet.net>
Reviewed-by:Frank Henigman <fjhenigman@google.com>
Signed-off-by: Chad Versace <chad.versace@linux.intel.com>