Fix bug where kai_get_m_step returns the incorrect value

Fix issue in kernels
- matmul_clamp_f32_f32_f32p16vlx1b_1x16vl_sme2_mla
- matmul_clamp_f32_f32_f32p2vlx1b_1x16vl_sme2_mla

where kai_get_m_step returns the incorrect value.

Signed-off-by: Jens Elofsson <jens.elofsson@arm.com>

Approved-by: Emil Ohlsson <emil.ohlsson@arm.com>