CODEOWNERS: Add entry for stm32 QSPI driver

I would like to add myself (@lmajewski) as the code owner for
stm32's QSPI driver.

Signed-off-by: Lukasz Majewski <lukma@denx.de>
diff --git a/CODEOWNERS b/CODEOWNERS
index 6022690..3b6e806 100644
--- a/CODEOWNERS
+++ b/CODEOWNERS
@@ -246,6 +246,7 @@
 /drivers/ethernet/phy/                    @rlubos @tbursztyka @arvinf
 /drivers/mdio/                            @rlubos @tbursztyka @arvinf
 /drivers/flash/                           @nashif @nvlsianpu
+/drivers/flash/*stm32_qspi*               @lmajewski
 /drivers/flash/*b91*                      @yurvyn
 /drivers/flash/*nrf*                      @nvlsianpu
 /drivers/flash/*esp32*                    @glaubermaroto