net/mlx5e: Fix NULL deref in mlx5e_tir_builder_alloc()

In the Linux kernel, the following vulnerability has been resolved:

net/mlx5e: Fix NULL deref in mlx5e_tir_builder_alloc()

In mlx5e_tir_builder_alloc() kvzalloc() may return NULL

which is dereferenced on the next line in a reference

to the modify field.

Found by Linux Verification Center (linuxtesting.org) with SVACE.