net/mlx5e: Fix NULL deref in mlx5e_tir_builder_alloc()

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.

Fixes: a6696735d694 ("net/mlx5e: Convert TIR to a dedicated object")
Signed-off-by: Elena Salomatkina <esalomatkina@ispras.ru>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Kalesh AP <kalesh-anakkur.purayil@broadcom.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Gal Pressman <gal@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>