msm: pcie: correct PCIe target link speed mask macro

When setting target link speed, it is correct to use
PCI_EXP_LNKCTL2_TLS instead of PCI_EXP_LNKCAP_SLS and
PCI_EXP_LNKSTA_CLS. All 3 macros have the same value defined
but it is proper to use the right one.

Change-Id: I5d99a696168170adf8dc577a6bf1fceb4fe82686
Signed-off-by: Tony Truong <truong@codeaurora.org>